1. Field of the Invention
This invention relates to flat panel devices such as a flat cathode ray tube (CRT) display. More particularly, this invention relates to a spacer structure for internally supporting a faceplate structure and a backplate structure of a flat panel device.
2. Related Art
Numerous attempts have been made in recent years to construct a flat CRT display (also known as a "flat panel display") to replace the conventional deflected-beam CRT display in order to provide a lighter and less bulky display. In addition to flat CRT displays, other flat panel displays, such as plasma displays, have also been developed.
In flat panel displays, a faceplate structure, a backplate structure, and connecting walls around the periphery of the faceplate and backplate structures form an enclosure. In some flat panel displays, the enclosure is held at vacuum pressure, e.g., typically 1.times.10.sup.-7 torr or less. The faceplate structure includes an insulating faceplate and a light emitting structure formed on an interior surface of the insulating faceplate. The light emitting structure includes light emissive elements such as phosphor or phosphor patterns which define the active region of the display. The backplate structure includes an insulating backplate and electron-emitting elements located adjacent to the backplate. The electron-emitting elements are excited to release electrons which are accelerated toward the phosphor, causing the phosphor to emit light which is seen by a viewer at the exterior surface of the faceplate (the "viewing surface").
In vacuum pressure flat panel displays, a force is exerted on the faceplate and backplate structures of the flat panel display due to the differential pressure between the internal vacuum pressure and the external atmospheric pressure. If unopposed, this force can make the flat panel display collapse. The faceplate or backplate structure of a flat panel display may also fail due to external forces resulting from impacts sustained by the flat panel display.
Spacers have been used to internally support the faceplate and/or backplate structures. Previous spacers have been walls or posts located between pixels (phosphor regions that define the smallest individual picture element of the display) in the active region of the display.
Spacers have been formed by photopatterning polyimide. However, polyimide spacers may be inadequate because of: 1) insufficient strength; 2) inability to match the coefficient of thermal expansion of polyimide with the coefficient of thermal expansion of the materials typically used for the faceplate (e.g., glass), backplate (e.g., glass, ceramic, glass-ceramic or metal) and addressing grid (e.g., glass-ceramic or ceramic), resulting in breakage of the display; and 3) low required processing temperatures. With respect to item 3), the low processing temperature requirements prevent the use of higher process temperatures throughout the display assembly. The low temperature tolerance prevents the use of assembly methods and materials in the display that would otherwise be available. Examples of such methods and materials include: high reliability sealing frits, high temperature getter flash methods, and fast, high temperature vacuum bake outs (which reduce manufacturing costs).
Spacers have also been made of glass. However, glass may not have adequate strength. Further, micro-cracks that are inherent in glass make glass spacers even weaker than "ideal" glass because of the tendency of micro-cracks to propagate easily throughout the glass spacers.
European Patent Publication 580, 244 A1 describes glass spacers provided with the following items: (1) a high-ohmic material (10.sup.9 -10.sup.14 ohms/square) coated on a spacer edge adjacent to the backplate structure (2) a patterned low-ohmic layer coated on a spacer edge adjacent to the backplate structure, (3) a conducting layer coated on a spacer edge adjacent to the faceplate structure and (4) a coating having a low secondary emission coefficient formed over the entire spacer surface, including any layers provided by items (1), (2) and/or (3). The low secondary emission coefficient coatings of item (4) include polyimide, titanium dioxide (TiO.sub.2), or a suspension including chromium oxide (Cr.sub.2 O.sub.3) particles, glass particles and an organic binder such as isopropanol.
For any spacer material, the presence of spacers may adversely affect the flow of electrons toward the faceplate structure in the vicinity of the spacers. For example, stray electrons may electrostatically charge the surface of a spacer, changing the voltage distribution near the spacer from the desired distribution and resulting in distortion of the electron flow, thereby causing distortions in the image produced by the display.
It would therefore be desirable to have a spacer which is capable of adequately supporting and separating the faceplate and backplate structures while controlling the voltage distribution between these structures. It would also be desirable to have a spacer having a thermal coefficient of expansion which can be matched to the thermal coefficients of expansion of the faceplate and backplate structures. It would further be desirable to have a spacer which is easily manufacturable.